1. Field of the Invention
The present invention relates to an improvement to a crankshaft rotation structure for a four cycle engine.
2. Description of Related Art
Referring to Japanese Patent Publication No. 2629936, FIG. 10 discloses, a cylinder a, a crankcase d, a sidewall e of the crankcase d, a crankshaft bearing i provided in the sidewall e, and an oil jet h provided in an upper part of the crankshaft bearing i of the side wall e for cooling a piston b.
The above described crank shaft bearing i is a single row bearing. Furthermore, the bearing has a large outer diameter. As a result, the attachment position of an oil jet h provided outside of the crankshaft bearing i becomes greatly separated from the crankshaft center. The piston b should be separated from the crankshaft center so that when the piston b is at a bottom dead center position, it does not interfere with the oil jet h. Accordingly, it is necessary to raise the piston to avoid the oil jet h. As a result, since the distance from the crankshaft center to a cylinder head attached to the cylinder a is increased, the size of the engine must be increased.